When I parallel two 120volt generators together into a 50 amp 4 pin plug do I get two 120 volt legs that are in phase or do I get two 120VAC legs that are 180 out of phase which would result in 240VAC being available on the outputs of the 50amp connector. If the two legs are in phase, are they locked together with no phase difference so they will no fight if they are connected to the same circuit?
Paralleling 120VAC generators
- Thread starter CraigBu
- Start date
craigav
Senior Member
Most I have seen maintain 120v (no 240v). What make\model generators do you have? If you are using the kit made for these generators, there should be no issue keeping the frequency in sync between the two. ~CA
craigav, thank you for your reply. Here is the genesis of the question. If you look at the 4 pin 50 amp connector in your house that is used for your stove, you will find there is 240VAC across two of the terminals. When you parallel two generators together, (in my case Westinghouse dual fuel 4.5KW) the paralleling cable has the same 50 amp plug that is used for a welder or stove. There could be two separate paralleling topologies.
Synario 1. The two generator are in phase. This would not give 240volts on the 4pin connector precluding you from backfeeding a house through a welder or oven or any other 4 pin 50 amp connector. Furthermore, if the two legs were not closely sycned in phase, there is a number of household appliances (your computer for one) that may not work well with the noise power created by the two legs being slightly out of phase.
Synario 2 The two legs are 180 degrees out of phase. Now you have 240 volts AC at the 4pin 50amp connector. I have not looked at campground power to see if the 50amp sources at the pedestals supply 240VAC or two 120VAC legs that are in phase.
I ask this because it would be nice to know if you can use two paralleled generators to provide power to a 240VAC system. I know I am being lazy and asking instead of getting the volt meter or o'scope out to look. But I appreciate the collective experience of those on this forum.
Synario 1. The two generator are in phase. This would not give 240volts on the 4pin connector precluding you from backfeeding a house through a welder or oven or any other 4 pin 50 amp connector. Furthermore, if the two legs were not closely sycned in phase, there is a number of household appliances (your computer for one) that may not work well with the noise power created by the two legs being slightly out of phase.
Synario 2 The two legs are 180 degrees out of phase. Now you have 240 volts AC at the 4pin 50amp connector. I have not looked at campground power to see if the 50amp sources at the pedestals supply 240VAC or two 120VAC legs that are in phase.
I ask this because it would be nice to know if you can use two paralleled generators to provide power to a 240VAC system. I know I am being lazy and asking instead of getting the volt meter or o'scope out to look. But I appreciate the collective experience of those on this forum.
craigav
Senior Member
Not to go too deep into the terminology as 240VAC in a house is actually a single phase and the 120V is derived from a split of that single wave at the center neutral tap in the transformer. (Split-Phase service).
In any case, these inverter style generators with parallel capability are designed to sync the frequency between the two inverters and as a result you will get twice the output wattage capability and remain at the same voltage (120v). So it will still be 120V and for the 50A outlet as the manufacture simply ties both legs together similar to a 30A to 50A adapter. If you were to measure between the two hot legs in the 50A receptacle from the inverter parallel kit you should measure 0 volts as both sides are electrically one in the same being connected to each other but 120V from either back to the neutral.
A properly wired common RV 50A receptacle at a campground or installed at home will measure 240VAC across the two legs and 120V from each leg to neutral (the neutral is where the split occurs).
To be succinct, the two inverter generators paralleled (or not) would still not provide 240VAC service to your house. If you had a 240V requirement for your house during a power outage (as an example) you would be better off purchasing a 240V generator although if the 240V was needed for something specific with a surge wattage requirement less than the generators can provide, such as a low horsepower 240V well pump, you could use a boost transformer to bring the 120V up to 240V and power the 240V pump motor with a 120V generator source via the boost ability of the transformer. ~CA
In any case, these inverter style generators with parallel capability are designed to sync the frequency between the two inverters and as a result you will get twice the output wattage capability and remain at the same voltage (120v). So it will still be 120V and for the 50A outlet as the manufacture simply ties both legs together similar to a 30A to 50A adapter. If you were to measure between the two hot legs in the 50A receptacle from the inverter parallel kit you should measure 0 volts as both sides are electrically one in the same being connected to each other but 120V from either back to the neutral.
A properly wired common RV 50A receptacle at a campground or installed at home will measure 240VAC across the two legs and 120V from each leg to neutral (the neutral is where the split occurs).
To be succinct, the two inverter generators paralleled (or not) would still not provide 240VAC service to your house. If you had a 240V requirement for your house during a power outage (as an example) you would be better off purchasing a 240V generator although if the 240V was needed for something specific with a surge wattage requirement less than the generators can provide, such as a low horsepower 240V well pump, you could use a boost transformer to bring the 120V up to 240V and power the 240V pump motor with a 120V generator source via the boost ability of the transformer. ~CA
As an applications engineer for 10 years for Cummins standbye power systems I agree with 90% of what you say. Split phase is a very generic term that has been handed down through the generations. Yes, household power is commonly referred to as split phase because you split two separate phases off of the 240 input to create the A side and the B side of your panel. If you look at each of the hots compared to the neutral you will see two distinct 120 volt legs that differ in phase by 180 degrees.
Your summary of the paralleling architecture is spot on. I only wish they would give more control so I could create 240VAC by running them out of phase. Pertaining to syncing the generators, I am not sure where it happens on an inverting generator. Must be where they synthesize the 60 hz and it is done with solid state vs speed bumping the generator to match up.
Not being contrary, you gave me some things to think about and I agree with what you say.
Your summary of the paralleling architecture is spot on. I only wish they would give more control so I could create 240VAC by running them out of phase. Pertaining to syncing the generators, I am not sure where it happens on an inverting generator. Must be where they synthesize the 60 hz and it is done with solid state vs speed bumping the generator to match up.
Not being contrary, you gave me some things to think about and I agree with what you say.
Kevin Cooper
Senior Member
I’m sorry to jump in, but Craig is correct. No 240 volts from those two inverter generators paralleled.
Now for the whole 180 degrees out of phase this is a correct statement ONLY if you say “On an oscilloscope”. No matter how you slice it, it is single phase. A sine wave is every 1/60th of a second in North America. A sine wave is a point in time. There are 3 sine waves happening at exactly that “same point in time”. L1 to L2 is 240 volts, L1 to N is 120 volts, and N to L2 is 120 volts. All starting and ending at exactly the same time. The direction of flow from each part of the coil, Must be in the same direction as it is connected that way, and there is only one phase primary coil in the transformer.
Now for the whole 180 degrees out of phase this is a correct statement ONLY if you say “On an oscilloscope”. No matter how you slice it, it is single phase. A sine wave is every 1/60th of a second in North America. A sine wave is a point in time. There are 3 sine waves happening at exactly that “same point in time”. L1 to L2 is 240 volts, L1 to N is 120 volts, and N to L2 is 120 volts. All starting and ending at exactly the same time. The direction of flow from each part of the coil, Must be in the same direction as it is connected that way, and there is only one phase primary coil in the transformer.
craigav
Senior Member
Most oscilloscopes share a common ground (neutral) across all channels which gives the "appearance" that there are two phases, some high dollar scopes have "isolated" channels which would show (if properly connected) that the phase for L1 and L2 is the same and is a single phase.
I have stated to some in the past that a way to consider this 180 degree oscilloscope "apparent" difference is similar to if you go to the beach and walk out say 100 feet, and if you face away from the beach you will see that the waves are coming at you, and then if you turn 180 degrees and face the beach you will see that the waves are going away from you. However the wave's direction never changed as they were always going the same direction and what actually changed 180 degrees was the direction of your observation. ~CA
I have stated to some in the past that a way to consider this 180 degree oscilloscope "apparent" difference is similar to if you go to the beach and walk out say 100 feet, and if you face away from the beach you will see that the waves are coming at you, and then if you turn 180 degrees and face the beach you will see that the waves are going away from you. However the wave's direction never changed as they were always going the same direction and what actually changed 180 degrees was the direction of your observation. ~CA
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Kevin Cooper
Senior Member
Great analogy Craig! It explains what really happens perfectly. But there will be many that will say we are wrong. If they were correct and were 180 out of phase, L1 to L2 would be zero volts.
... not me, because I don't understand what you're talking about. I'm happy when I get my flashlight working. But it's comforting to know we have excellent electrical minds on the forum and they are willing to share their knowledge.
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